The invention pertains to machine vision and, more particularly, to methods and articles of manufacture for inspecting ball grid array devices.
In automated assembly processes, such as those for assembling electronic circuit boards, it is important to determine the exact location of components prior to their placement for final assembly. For example, an assembly system must know the axial position and angular orientation of each component before placing its leads on appropriate solder pads of a printed circuit board.
Accuracy in positioning is ever more critical as the ratio of the size of the electronic components to the number of conductive leads increases. Such is the case with ball grid array (BGA) devices. These are small surface mounted devices containing tens or hundreds of conductive solder "bumps" arranged in regular patterns, e.g., rectangular arrays, "checker boards", et cetera. Because the bumps are so closely spaced, accurate placement and alignment with solder pads on the circuit board is imperative.
The art suggests a few approaches to determining the orientation of BGA devices. These approaches are primarily binary techniques based on "blob" analysis of the solder bump array images. A drawback of the approaches is that, due to their binary nature, they are highly susceptible to lighting conditions or device-to-device variations. Moreover, they require that correspondence steps be performed to remove extraneous features, or noise. Those correspondence steps are typically very time consuming. While some approaches have attempted to reduce that time by limiting the correspondence step to a small subset of the bumps, those approaches suffer reduced accuracy.
An object of this invention is to provide improved methods for machine vision analysis and, particularly, improved methods for inspection of ball grid array devices.
A more particular object of this invention is to provide improved methods for BGA device inspection that permit the placement and orientation of those components to be readily and accurately determined.
Yet still another object of the invention is to provide such methods that can execute quickly, and without consumption of excessive resources, on a wide range of machine vision analysis equipment.
Still yet another object of the invention is to provide articles of manufacture comprising a computer usable medium embodying program code for carrying out improved such methods.